Activation of Actinyls to Generate Actinide Nitridos, which Activate CO2 to Regenerate the Actinyls
Résumé
Gas-phase reactions of actinide complexes enlarge the scope of accessible chemistry of these elements, and provide insights into bond activation that may be unattainable or incomprehensible in condensed phases. The distinctive actinyl moieties—hexavalent AnVIO22+ and pentavalent AnVO2+, where An = Pa, U, Np, Pu or Am—present robust oxo bonds that are particularly resistant to activation. Actinyl activation by isocyanate ligands in anionic complexes has been achieved by endothermic reactions (1) and (2).
[UVIO2Cl2(NCO)]- → [NUVIOCl2]- + CO2 (1)
[NpVO2Cl(NCO)]- → [NNpVOCl]- + CO2 (2)
The computed potential energy profile for reaction (1) predicted that the reverse reaction should occur in the absence of excitation. Remarkably, it was demonstrated that the uranium nitrido does indeed spontaneously activate CO2 to regenerate uranyl. A central goal in actinide chemistry is to identify and understand variations across the series. Reaction (2) is evidently more facile than (1), which may reflect stronger U=O versus Np=O bonds, and furthermore indicates lower kinetic barriers to activation of neptunyl(V) versus uranyl(VI). Relativistic multireference computations are underway to understand this difference in reactivity. Other experimental/computational targets include activation of plutonyl(V/VI) and americyl(V) for comparison with the lighter congeners, and ultimately to provide guidance for condensed phase synthesis.
[NpVO2Cl(NCO)]- → [NNpVOCl]- + CO2 (2)
The computed potential energy profile for reaction (1) predicted that the reverse reaction should occur in the absence of excitation. Remarkably, it was demonstrated that the uranium nitrido does indeed spontaneously activate CO2 to regenerate uranyl. A central goal in actinide chemistry is to identify and understand variations across the series. Reaction (2) is evidently more facile than (1), which may reflect stronger U=O versus Np=O bonds, and furthermore indicates lower kinetic barriers to activation of neptunyl(V) versus uranyl(VI). Relativistic multireference computations are underway to understand this difference in reactivity. Other experimental/computational targets include activation of plutonyl(V/VI) and americyl(V) for comparison with the lighter congeners, and ultimately to provide guidance for condensed phase synthesis.